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nonnen nenne' "Linn onlrronnre, einer rennt, Ansinnen ro rif-rr. Linn Manerasrnnrrro eonroialirron', or rl/ronnie, new roert, a eouronarron or new ironic rnfaoron.

.Application filed May "i3,

'lhe invention is rnore partirularly ad dressed to tractors of the l' `avy hauling; type. embodying 'front steering' n ieels or sleds and rear traction elements ot the track-layingr type. Atractor ot this nature is disclosed in lrletters Patent 1.270.531. granted to llohnan llarry Linn, elune 25, 1918.

'llo adapt the tracir-layingr .ractor to `co1n niercial hauliu'o. two inajor shortcomings oft the `general-utility type niust be eliminated, namely, the loss olf traction under various circunistances; and. the element ot risk attendant upon hauling; downgrade or upon backing-up. y

',lhfaetion may he lost and the load thereby stalled1 under the ltolloWingocireninstances:

il; llVhen the pull is heavy7 the tractor liits at the trent and rides only upon the rear part oit its tracks; tractive areais thereby reduced. the tracks slip and the machine is not propelled.

2. The condition of the ground being' conducive to slipping; ot the tracks and no convenient control ottraction being provided, the tracks slip `tor Want oli su'iicient pressure Vott the tracks upon 'the ground and consequently the load stalls.

rlhe surface ot the ground beine; uneven or covered'with rocks, logs, or other fobstructions, the tracks lose contact throughout the lgreater part ot their length; tractive area being thereby reduced7 the tracks slip and i stall the load; y

e 4;. lWhen `the inside track is deelutchecl on a sharpturmuthe 'lull power is Vthrown on the outside track; this slipabeingg only one-halt et the normal tractive area, andthe load stalls. y

lhe solution oit problen'i` l requires not only a traction inernber oit such flexibility that it Will keep the tra" k on the ground even though the torque tends to litt the `front olfv the nia- .chine, but also depends on a heavy Weight carried 'tar in advance ol: the track. and which.. through the great leveragfe afforded, will n'iake it impossible Ator the track to lose its bearingr onthe ground rlhe logical Weight to `carry forward isvthe power plant. This places the motor, radiator. clutch. transmis sion and controls` in positions of convenience and accessibility'. lt further admits oft their protection from excessive vibration through the niediurn of suitable springs and rubber tires. f y

ylphe solution of problein 2' is simplitied by reali. serial no. nenes.

the preceding disposition. Since traction is dependent not only upon the area of ground Contact oli the tracks, but equally upon lthe .pressure otl the tracks on the ground. it tollows th at increasing; the Weight onthetracks increases their tractive effect. The logical .Weigllt to carry over the tracks, in the space lett clear by the removal or the power plant7 etc., is pay load. Such load. (or dead-.Weight when incre convenient) can be varied-'as oeeasion requires. This makes it possible ,to eliminate all dead Weight inthe design of the machine. thus econoniizinn in fuel consumo tion and general Wear and tear when the inachine running' light.

'llhe solutiouo't problem 3 presupposes the achievement ot a traction ineinber ot' such itleiribility that it will nmintain normal contact with veryuneven ground. This involves a departure troni customary practice, but, in the case ot the inventive concept hereinafter described, resultsnot only in a cornpletely flexible unit. but one in which Weightcarryinn' arles and axle bearings are eliininated. rllhe importan ce oli gettingrid of these delicate parts in a unit- Which, ot neeessitv. Works most o'l' the tin'ie in mud, sand arid Water is lnanitest;

Problem 4l can be solved practically only by doing away with track steerage; using' conventional Wheel stceragre (inadepossible by the long; chassis evolved in the solution of prohleiu l). 'liull power may be applied to both tracks under all conditions through the customary di fferentlial gear. lin the automotive vfield the ditlereutiil practically a per :tected inechanisin,` beinp; less likely to give trouble than almost any other part of theV inachine. Vllhe elimination o'll track` Steerage means netting,1 rid ot a clutch and brake on each track and the separate controls lor each ot their.. lt does array With the Wear and tear dependent upon there and the mainte nance the).T require.

Finally.. there is the question ot risk at tfnidantupon hauling down 2efradeor upon backingr rp` llt is a concomitant ot track steeragre. This torni o't steeragge requires that Whenever the tractor is backingf up or Whenever it is holding; back a load on a. down flrade` the controls must be operated the opposite of normal. lin normal driving'. it the machine start-s to veer olli the road to the' riejhti the driver turna his controls to the lett and' the inachine resumes its proper course. Bun 1i Vthe ri ght as though to turn the machine further oil" the road. If he forgets, or makes a slip yin a moment of excitement and turns .his controls the natural way, the machine will run ofi the road. Precisely the same thing,r is true when backing the machine. rFhe fact that the driver has to remember on each down `grade to work his controls the wrong way, so to speak. constitutes a real menace when arheavy load is coasting fast down grade; if the driver. in a forgetful moment. or from force of habit, operates the controls in the normal manner. the machine and load will leave the road. .lt is particularly difiiculttor driver to keep his head on a rolling' down `grade where the tractor is first holding back the load..then pullingf it, and so on. Each time the'load changes from a pull to a push and vice versa` the driver must change his method of operation. The replacement ot track steeraeje with wheel steerafre does away with the danger of handling loads on down grades because. as is well known 'from car and truck driving. wheel Steerage works the .same vway under all conditions.

The propositions stated are the resultof actual demonstration over all sorts of terrain, from theA ice and snow conditions oi' the north woods. the heavy sands of desert reveionsthe'emulsified soil ot the oil fields, and over the Iround peculiar to mining districts. snaar and rice plantations.

With the foregoing; vin mind, and retaining the general principle of the tractor of my former patent, the ohiects of the present invention are to provide a load carrying and hauling machine' capable of successfully meeting the most difficult hauling conditions,

'including the hauling of trains ot sleds. semitrailers and four-wheel trailers; to provide a machine adapted for heavy hauling, and to provide other novel fea-tures as hereinafter described and finally claimed.

The invention is illustrated in the accompanying drawings, in which,

'Fim S' is a View in elevation ofthe runner blocks, showing same in cooperative relation,

Fig. '9 is a bottom plan of the same. Fig. 10 is an end view of one of t-he'runner blocks,

Fig. 11 is a section on line 11-11 of Fig. 9,

Fig. 12 is an elevational view of a section of the roller assembly,

Fig'. 13 is a sectional view thereof,

Fig. 14 is a perspective view of one of the journal pins for the rollers of the roller assembly,

Fig'. 15 is a plan view of connected track or lag' plates,

Fig. 16 is a side elevation of the same,

Fic'. 17 is a perspective view of one of the lag' pins,

Fig. 1S is a detail showingl the method ot securing the pin,

F'b'. 19 is a` bottom view of one ot the tracks or lap` plates,

Fie: 2O is a section on line 20-20 of Fig. 19,

Fig. 21 is a sectional view of a lag plateI with i roller in tracking relation,

Fig. 2Q is a perspective view of au emergency ice creeper,

Figi. 23 is a. plan view of the compensatinjY slide for the idler sprockets,

Fig. Q-lis a .side view thereof,

Fi2125 is a section on line 25m2?) of Fig'. Q3,

Fig. 26 is a section on liuc 26---26 of Fig. Q3,

Fig. Q7 is a sectional view of a driving,r sprocket,

Figs. QS. 29 and 30 are diagrauuuatic views, eraphically illustratingr the complete flexibility of the tracks under irregular ground conditions.

The present invention is directed primarily to ay heavy-hauling severe service tractor of the self-laying track type, and the vehicle details, aside from the means employed to secure maximum traction efficiency, may he of any approved type. For the purposes of the present invention, such details, shown more particularly in Fig. 1, may he summarized as a main frame 1, having front wheels or steering supports 2, steering,Y mechanism 3, transmission 4, drive shaft 5, universals 6, and differential 7. As indicated, there is an unusually long wheelbase. with the power plant well forward, the tracks at the rear, and a platform or clear space over the tracks for variable loadingY to insure the necessary pressure ou the tracks.

rlhe main frame 1 is provided throughout the rear extension thereof with au.\:iliary frame bars 8, secured in spaced parallel relation to the main frame bars by cross hars 9. Hangers 10 secured to the auxiliary and main frame bars, accomn'iodate a transverse shaft 1l., the ends of which form pivotal or trunnien mountings for load transferring elements or rocker beams 19.. The rocker heams 12, shown more particularly in Figs. 4 to 7 inclusive, comprise open triangular castings, with bearing' sleeves 13 at the apex to engage the shaft 11, and spaced dependingr base connected walls 14. The bases of the walls 14 have lateral extensions or ledges 15, hraee ribs 16 being provided to strengthen the struclili " bil lill neonato tureas awholfe: "lllhelbearing sleeves taire the ing' movement Whilel beine' held against lateral movement. ll't Willi be noted" that the axis' of the sliaft securing' eleinent or sleeve ll ofthe rocher beanr is located rearwardly of a line dividing the roelv r beam fore andT aft. 'lihis results in a didierential bottonr bearing area, the forel extension exceeding` inl area the bearing area of the aft extension. 'lhis is' of importance in considering` the rel-a tieni of the runner blocks which absorb and transmit all load and" other stresses in'rposedv upon the` rocker' beam. rll`he ledges lili have notched or' arcuate depressions li, therebeinga plurality of such depressions inthe fore extension to provide for relativeV adjustment of the front runner hfoclr. 'ifi-ieA described notches or depressions constitute half caps or bearings forV the trunnion` or pivotal ele inents 'lil of a coinplernentalu set of runner blocks f2), which support the rocher'beain fore and aft. Evidently, this construction and' assembly admits of 'vertical swinging neoveinent only.

The runner blocks i9, shown more particularly in Figs. d to il, inclusive, are arranged in pairs in tandem fashion for each rocher beam, with their opposed inner ends innnediately adjacent or lapping` and their outer ends Well beyond the ends of the rocher beain. rllhe runner bloclrs are of substantially vtriangular forni in sidey elevation, with their ends rounded and their upper surfaces down Wardly inclined ln sho-rt, the apices of the runner blloclis are in confronting or overlapjgiing relation. 'llheelenicnts or pintlles f8 of the runnerbloclrs project laterally from huh formations 9,0 thereof7 the arrangement being such that when the runner bloclrs are junta posed with relation to the forked ends of the rocher beam, thepintles i8 are accommodated in the proper depressions or beairingl cavities of the rocker 'beaux and are properly retained by straps or lll bolts 2l, penetrating vertical openings 2Q, in the roclrer beain.

V"lhe substantially straight bottom Walls of the runner blocks are formed with a cent "al longitudinally disposed rib or rail Q3 continued at the rounded ends of the blocks and finally vanishingin thebody thereof,the downwardly inclined or converging upper Walls of the blocks presenting substantially intact or plane surfaces. rlllhere is thus provided a differential roller path for the rollers Which transfer the load and other stresses from the runner blocks to the tracks. 'lhe provision of a. pluality of half caps or bearings, that is to say, the arcuate depressions "il, in the fore extension of the rocker beam obviously ac inits ofendivise adjustment of the forward runner block with relation to its mate in order to adjust the chain of rollers in accordance iivotal or swing# with fit and. Wear.1 lt is important 'that the roller pathi represented by the rail or rib 23 be maintained throughout the lower entreini-i tire of beth runner bloelts. Hence, there is a rib extension 2t on the opposed endsof'the riilnnerblioclrs5 sothat at thispoint, and for all relative adjustments7 the ribs of the cooperatin runner bloels will overlap. 'lflnou gli out the extended lengthsof the ribs 2?, they are relatively inclined in plan and slightly divergent in vertical' direction toward the bottoni, as shown in Figs. 9' and' ll. 'lihis arrangement provides a substantially un! broken or continuous roller path of uniformi Width in the lapped ends of the runner blocks, notwithstanding their* longitudinal adjustnient. lihe tapered nose construction also provides for articulation of the confronting portions of the runner blocls under varyingeonditions ofterrain,

lr roller chain 25 is adapted and arranged for travel over the described differential roller path of the runner blocks, to eliminate friction between the runner blocks and the tracks. 'llhe roller chain is of unique and peculiar forni in that the rollers are of the flanged or spool type' to provide a reduced annular surface for cooperation with the rail of the runner blocks, and relatively enlarged annular bearing surfaces for cooperation with other parts of the runner blocks and the tracks or lagebeds. The effect and inerit of this is to inal're the rollers independent of the speed of the track and to relieve the axles or spindles of the rollers of load thrusts, thereby ensuringl inaxiinuinroller lfiearing efficiency. lt further results in increased life and economy through the obviously reduced speed of the rollers. Y

\ 'llhe roller chain, shown niereparticularly in Figs. 1Q and 13,' is made up of rollers of the spool type connected in pairs, each roller comprisingI a hollen7 spindle 26 and -end flanges 2T, Wl'iereof the spindle Vcooperates with the rib 23 andthe flanges with the tracks and with unribbed portions of Vthe runner blocks.

The rollers are connected by side bars 2T, having1 integr-ral half bushings Q8 adapted for reception of the spindles of the rollers. Gonnecting links 9 connect adjacent rollers of respective pairs, through the medium of pins `30, p assing' through the bushings 2S and links 29, and terminally upset beyond the latter, as clearly shown in 13. The ends of the pins, l? le, have fiat faces 3l, to engage corresponding;` slots 32 in the connecting links. rllhe sel'llaxyiug` ti-'aelr n'icinlier, hereinafter referred to sin'iply as the track, is niade up of a pluralityT of linked lap; plates of peculiar forni. They are shown incre particularly in Figs. l5 to 2l inclusive. ylhe lag,` plates are substantially dat skeleton structures 38, having" their ground contacting surfaces essentially interrupted, as hereinafter described in lil) detail, to provide the necessary ground grippingor tractive properties. Each lag` plate is a solid manganese steel casting of generally fork design, Fig. 19, including a main body portion 34 and spaced side elements 35 joined to the main body portion 34 by raised portions or ribs 36 and tubular terminals or eyes 37.

At the opposite end, the main body portion 3% is formed. With an eye 38, and the side ele,- ments are formed with eyes 39. ltis a merit of theinvcntion that the eyes 39 are bnttressed by marginal right, angle extensions 40 ot the cross ribs 36 Y;' that the eye 38 is buttressed by longitudinal ribs il oining them to the ross ribs; and that the eyes 37 are buttressed by marginal ribs 4t2 branching from the cross ribs. i The eyes 37 are 'further reinforced by a permanent grouser i3 consisting of a V shape oficset,the apex of which is located about mid- Way of the main body portion and the arms Vof which extend to the remote corners of they eyes 37. To further provide for efiicient gripping as Well as to establish substantially'nnitorm distribution of metal to insure uniform heat treatment of the casting, the side elements 35 are out away at their tor- Ward end in. line With the eyes 37, this reduction being external, as at lle, and tending to define the ribs Z12; there is likewise at the other end an internal reduction 45, defining the rib l0. and stopping shortioic the eyes 39. So also, the main body portion 34 is embossed as at 46, between the cross ribs and the central eye 38; the cross ribs are slotted as at 47; and the permanent grouser is defined by its continuous or uninterrupted offset relation With surrounding` depressed metal and by the gaps between it and the cross ribs. This permanent grouser is of greater depth than the ribs or other offset portions and its greatest depth is at its apex or in the central region of thebody 341, the arms of the grouser ygradually inclining towards the eyes37. T he main body portion Y34 and the side elements 35 have bolt openings i8 in their ribbed or padded areas. Under adverse road conditions, as when encountering ice, provision is made te increase the grip of the lag plates Y through the use of. readily attachable and detachable ice Creepers 49, shown in dotted lines in Fig. 19 and in detail in Fig. 22. They are integral angle members embodying an attaching` Wall 50 anda grippingivall 51 reinforced byiwebs 52. "The Wall 50 has bolt holes 53,

which register with the openings 48 of the lag plate, and bosses 5e, which are accommodated in the slots 4:7 ot thecross ribs. The creeperis bent as at '55 to adapt it to take a bearing against lthe permanent grouser, and this Varrang'ement and thefact that the bosses 54 haveV a bearing in the lag plate operates to prevent or` minimize thrust on the bolt connect-ions.

'The inner surface or floor of each lag plate,

has a longitudinally ranging hump or raised portion 5G in the main body portion, which, in conjunction with identical sets ot ribs 57 and 58, define parallel tracks or flange-nays for the ilangesof the anti-trictimi rollers, the height oia the ribs being so regulated that the spindles ot the rollers are clear ot or out olf Contact with the tracking area. It will be observed, upon reference to Fig. 21, that the construction and arrangement are such that side thrust et the rollers is absorbed on both sides ot the respective roller flanges by the ribs 57 and 58. Upon reference to l? .16, it will be noted that the ends 59 of the ribs 57 and 58 overhangor extend beyond the floor portion of the lag plate in order to provide with the next adjoining plate a substantially intact or unbroken iangeray. The noses ot the rib extensions are rounded, as at G0, to insure proper articulation. Evidently one ot the characteristics of the lag plate ot this invention is its lack of height and the way it hugs the ground. Since no lead is sullcred to be imposed upon the spindles of the rollers. there is no difiiculty in excluding mnd and grit, the ribs 57 and 58 operating efliciently as excluding elements notwithstanding that they are relatively close to the ground.

The eyes or hinge elements 37 ol' the lagr plates are staggered with relation to the ccntral eye 38 and eomplemental side eyes 39, to provide for proper linking ot adjoining plates. In order to secure them in link torination, I prefer to employ link pins 61, so disposed as to be fully floating whereby shearing and undue Wear are avoided. These pins. shown in detail in Fig. 17. are ot a diameter to tit the eyes or hinge elements, and in length exceed the Width of the plates. As shown in Figs. 17 and 18, each pin is provided near its ends with rounded slots G2 ot' the `tull diaineter of the pin, for the reception 'ot rivets G3, Which are driven downwardly through openings 64 formed in the side elements of the lug plates and retained by detorn'iation which causes them to hook into a bottom. depression 65. The. offset location of the'opening (i4- y and its elongation, causes the rivet when dri ven to take a slight radius G6 with respect to the slot or recess 62. Accordingly. although the pins are held against endwise movement by the rivets, the latter have no restraining influence against limited rotary movement of the pins. Hence. the pins ,being full floating with respect to the connecting eyes a highly efficient and durable connection is aflorded. It will also be observed With reference to the, linking of adjoining plates that the area of bearing surfacev afforded the pin is equally distributed and substantially continuous, vvhich further operates to prevent chafing or shearing of the pin.

The lag plates, when assembled in connected or track form, provide front and rear open` tessere ings 66 and 6'? on each side of the main body' of the uplate for the reception of sprocket teeth.

The tracks cooperate with seas of double u sprockets Wh-ereofthe rear sprockets titl are driving sprockets, and the forward sprockets 69 serve as ,idlers The latter are mounted for compensating movement to insure instant fand complete responsiveness of 'the track to lil successive changes of ground surface.

rllhe driving sprockets 68 are coincident or tivin spiders formed with a common hub 70 on an-axleil, supported in hangers on the main `andauxiliary frame bars. rlhe inner spider 'la `has a flange @constituting` an internal or ringgear 73, in mesh with a driving pinion .74. The latter is secured on a jack shaft 75 mounted in bearings depending from the main frame. rlfhe jack shafts are ofcourse an `operated in any appropriate manner through ithe differential 7, and thus the drivin g poiver istransmitted to the rear or driving; sprockets ofthe track. il i The `forvvard or idler sprockets 69 are like- 2.3 Wise of double spider construction. They are mounted in a compensatingslide frame, yieldable underspring control to permit the idler sprocket to move toward the driving` sprocle ets, -to vary the tension of the lag-bed in ae- :i0 cordance vvith varying,` ground surface conditions.

'The slide frame, shovvn Ain detail in Figs. 23 to `2G inclusive, includes side bars 76, 'formed with channels i7 in their relatively au outer yside edges, to receive the main frame ,flangmto thereby permit sliding movement of ythe, slide frame. The slideframe iits between the main and auxiliary frame bars and `slidably cooperates with each, and its bars lo are equipped With bearings 78 to receive the `.idler sprocket shaft. The forward ends of the side bars are connected by a head 79. llt `guide section 80 is arranged in advance of the headand formed centrally With an openi5 ing 8l, to receive a rod 82. The latter extends beyond the slide frame and through a bar 83 `secured to and transverse to the main and auxiliary frame bars, and beyond the bar 83 `passes through a strongr coil spring Sel, and is nu terminally provided nfith a head cap or dislf- `85 to bear on the end of the spring. rllhe respective ends of the rod 82 are threaded vfor the reception of nuts 86, which provide for manual adjustment.

rlhe slide frame, and thus the forward or idler sprockets are held in normal position by the spring 84e, but are permitted to move rearwardly against theresistance of the spring` under strain on the track.

The compensating-'slide carrying the idler sprockets permits-the track to yield in order to overcoinezground difficulties, Without sacrifice of traction effort. lt vvill be noted that the track underlies the rollers through the 15 combined length of the runner blocks, and to bfi tra

tue extent of this length the track has full bearingr on. the ground and thus traction'in accordance With the Weight of the load. This effective tractive length of the track is maintained under all operative conditions, but its characteristic line of application may be automatically varied by the ,ground surface. For example, referringi to Figs. 28, 2f), and 30, the differentirregular ground surface conditions have resulted in responsive compensating movements of 'the rocker beam, the runner blocks on the rocket-beam, and the rearward movement of the idler sprocket to provide the necessary increased ground contact of the track. rfhese elements are thus auton'iatically governed in movement by the character of surface vvith which 'the track engages at any particular moment, and in this compensation provide a perfectly flexible traction unit and more effort j ust when needed.

Referring4 again to the lag; plates, it will be noted With respect to the permanent grouser that the apex of the il is directed towards the rear in. the travel of the track. The merit of this is that it makes for tractive efficiency and for self cleaning because there is no tendency A'for it to pack,nor does it essay to push obstructions before it. Another advantage attendant on this construction is that it absolutely precludes side slippingon side hill Work or on crowned roads. i

The tracks are self-clearing in the event of building up7 conditions, namely, when rocks, ice, Wet snow or other substances are trapped between the sprockets and tracks. Such conditions are overcome by the responsive action of the compensating;` slide which ,permits the sprockets to slip to forcibly eject the trapped material. Moreover, the instant responsiveness of the slide to permit slippage of the. tracks will retard breakage due to conditi ons brought about through careless-- ness or ignorance of a green driver, as for example in bad going; and in lovv gear, when he steps on it.

llllhe `general design of the tractor, that is to say, its unusually long frame, With tracklaying drive at the rear and motor and steeragein front, gives in itself certain advantages. lFor example, it dispenses with steering clutches, steering brakes and their controls. Full. power is available on sharp turns. loth tracks drive around a turn and thus avoid cutting up the ground. rlhe suspension is such that no Weight is carried on any axle or axle bearingin the rear drive.

rlihe tracks may be said to be universal in that they are suited to all conditions of terrain, no special grousers or mud hooks being,r necessary` rlhey are flexible to th-c greatest possible extent, a feature very essential to maximum performance under varying conditions because it affords the tracks full contact with the ground at all times and prevents loss of potential pull. rfhe compensating loo lid;

' cast. manganese steel, and substantially uniform sections are provided to ensure proper heat treatment. For example, the flanges of the rollers, which must be especially resistant to shock and wear, are recessed as at 87, to provide tor uniformity of section, the recess beingl interrupted bywebs 88, which avoid undesirable unsupported overhang of the flanges.

laving described the nature and objects of my invention and the manner in Vwhich the same is to be performed, claim i. A traction unit having, in combination, a flexible track and its complemental supports and a system of load transmitting elements, including an axle-hungrocker beam and runner blocks on which it is superimposed, the runner blocks being capable of relative endwise adjustment and having' their confronting ends overlapping.

2. A traction unit having, in combination, a flexible track and its complemental supports, and a'system of load transmitting elements, including an aille-hung` rocker beam andrunner blocks on which it is superimposed, the rocker beam having bottom half caps or bearings to establish rocking engagementof the runner blocks.

3. A traction unit having', in combination, a flexible track and its complemented supports,eand a system of load transmitting` ele ments including an axle-hung rocker beam and wedge shaped solid runner blocks ou which it is superimposed, the runner blocks having each a central longitudinally ranging' rib and flanged rollers cooperating; wit-h said ribs and track and affording an `orbital path of movement between the track and runner .blocks, the construction and varralignment being,` such that no weight is imposed upon the spindles of the rollers.

4. A traction unit having a self-laying track, a roller bearing` for the track, and runner blocks with which said bearing cooperates, said blocks having' mitered ends and Leaders int)r traveling` over such blocks aud having a portion to cooperate with the trackway on the blocks, and a self-laying track engaging; a trackway portion of the roller bearing' of a dia-meter varying;` 'from that of the roller bearing/,i` engaging the runner blocks.

G. A tractor of the `front Steerage type equipped with traction units each having, in combination, an endless track ol the flexible type, means for loading the track and including pyramided elements capable of ver tical rockingv movement, a connected series oi? flanged rollers between saidl means and the rack and afforded an orbital path oil'i movement over mated rockingY elements, said track embodying` articulated lag plates having;- provisions for supporting the rollers by their flanges and not otherwise.

7. rlhe combination with the tracks and ruimer blocks providingY a differential roller path, of hollow rollers of the flange type, side bars having half bushings for the rollers and means for maintaining the assemblycomprisinev links and pins penetrating` the hushed rollers and button-headed in the links.

S. The combination with the tracks and runner blocks providing` a di li'ereutial roller path, of rollers of the hollow spindle flange type, the roller flanges having overhangs buttressed by radial webs.

9. A pair oi runner blocks each equipped with means whereby it may be suspended for vertical rocking; mort-meut and each havingy a bottom rib constitutiin;` a roller path. said runner blocks having tapered nor-:es in overlapping relation to permit articulation oli the blocks withoutinterrupting the continuity of the roller path.

l0. A rocker beam having` a sl cove-like supporting element with depending side valls, the bottoms ot which have depressions constituting half cups or bearings. A

ll. A rocker beam having,- an oil' center sleeve-like supporting` element, with spaced depending side walls, the bottomsI of the latter havingl depressions, and the ledaes of the walls being pierced lor the reception of retainingmeans.

l2. In a tractor equipped forwardly with steerage provisions :md with a power plant and equipped rearwardly with irai-tion units and with a final drive for propellingthe sames the combination of a load carrying platform above the traction units, articulated load transmittineelements between the traction units and said platform, said traction units having,` flansci'eways and said load transmittingq elements liaifiirgV ribs and rollers having; flanges adapted to said flan-neways and spindles adapted to said ribs.

ln testimony whereof I alli); my signature.

HOLMAN HARK Y LNN. 

